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FFT: factor a shuffle out of the inner loop and merge it into fft_permute.

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6% faster SSE FFT on Conroe, 2.5% on Penryn.

Signed-off-by: Janne Grunau <janne-ffmpeg@jannau.net>
(cherry picked from commit e6b1ed693a)
This commit is contained in:
Loren Merritt 2011-02-12 11:48:16 +00:00 • committed by Michael Niedermayer
parent 709946b34c
commit 11ab1e409f
6 changed files with 45 additions and 38 deletions
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9
libavcodec/fft.c
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@ -97,6 +97,7 @@ av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
if (!s->tmp_buf)
goto fail;
s->inverse = inverse;
s->fft_permutation = FF_FFT_PERM_DEFAULT;
s->fft_permute = ff_fft_permute_c;
s->fft_calc = ff_fft_calc_c;
@ -113,8 +114,12 @@ av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
for(j=4; j<=nbits; j++) {
ff_init_ff_cos_tabs(j);
}
for(i=0; i<n; i++)
s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = i;
for(i=0; i<n; i++) {
int j = i;
if (s->fft_permutation == FF_FFT_PERM_SWAP_LSBS)
j = (j&~3) | ((j>>1)&1) | ((j<<1)&2);
s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = j;
}
return 0;
fail: